Parasite could be cause of crab deaths

John DeSantisSenior Staff Writer

Friday

Mar 25, 2011 at 12:22 PM

BATON ROUGE — Blue crabs from Terrebonne Parish show a heavy infestation of marine microbes that clog the gills, making breathing difficult and, in some cases, impossible for the 10-legged creatures, scientific tests show.Signs of the lagenophrys protozoa could account for the increased number of blue-crab deaths reported by fishermen and crab buyers, who complain that many do not survive their trips to market.Scientists are also looking at the possibility an infectious disease called white spot. Those tests are under way.Parasites that affect crabs are generally not harmful to humans and are killed in the cooking process, scientists said.Additional complaints have been made of alarmingly low crab catches, but state biologists had no immediate response to that issue. The results indicating the microbes are preliminary and scientists at Louisiana State University continue to examine crab samples to determine the cause of the deaths. Marty Bourgeois, a biologist with the state Department of Wildlife and Fisheries biologist, told members of the Louisiana Blue Crab Task Force at its Thursday meeting that he received an email from LSU veterinarian John Hawke containing some information on his tests.“The preliminary analysis showed heavy infestations of protozoans,” Bourgeois said. “In crabs from Chauvin, we saw a little black spot at the top of the gills. Some are very black. These are protozoan, and they leave a little clear bubble shell.” The parasite clogs the gills and interferes with respiration, he said.Timmy and Trudy Luke of Luke Seafood in Dulac provided samples to the state, as did Wayde Bonvillain of Montegut. Both complained of crab die-offs. Bonvillain spoke to the panel, showing them crab samples he pulled from an ice chest.Just a 79 dozen of the 10,000 live crabs he bought in recent days survived long enough to either shed their shells for Bonvillain’s soft-shell customers or been sold live for boiling pots.“Seventy-nine dozen out of 10,000 crabs ain’t nothing,” Bonvillain said, explaining to task-force members that the purchases were made with money intended to pay taxes. The move was necessary, he said, to try and keep his plant going.Louisiana SeaGrant agent Alan Matherne said the microscopic parasites sometimes are found in a specific area or water body and are not unheard of in local waters.“Sometimes you don’t see them for a very long time,” Matherne said. Trudy Luke presented business records to illustrate that fishermen are bringing in far fewer crabs than she is used to seeing.“I have a printout of January. We are at a 48 percent loss,” she said.Task-force members said crab dealers in the east and west Louisiana are not experiencing die-offs like those in Terrebonne.“We are going to have to document it, that is all we can do right now,” said Chairman Gary Bauer, a processor from Slidell.Scientists said there is no way to determine how widespread the problem is within Terrebonne Parish.There was more potentially bad news for crabbers when SeaGrant fisheries specialist Julie Anderson presented her findings on oil-spill dispersants’ effect on crabs. In lab tests, she said, some concentrations killed crabs within 48 hours.Tulane University scientist Erin Grey related a related study her team did during the BP oil spill.The oil-dispersant mix, she said, is much more deadly to crabs than oil or dispersant alone.“One million gallons of dispersant was applied to the surface,” Grey said. “That’s the stuff we have to worry about when we are talking about blue crabs.”Grey’s team observed juvenile crabs at Grand Isle, Texas, Alabama and Florida.A disturbing aspect of Grey’s research was the observation of what she termed “unusual orange droplets” on the babies.“This was bright orange, like the color of Tang,” she said. “I’ve never seen anything like it before. These with the orange look a lot different than the normal ones.”Tests are under way to determine the chemical makeup of those droplets.“They don’t seem to be oil, and they don’t seem to be dispersant,” Tulane researcher Caz Taylor said.Of baby crabs sampled, Taylor said, 73 percent had the orange droplets.Taylor said much work remains to be done before the effects of the BP spill on crabs and other marine life can be determined, asking crab processors, fishermen and buyers for help with data, samples and other information that can shed light on present and future effects.“We need experts to help us work on this.”

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